The invention is directed to a method and to an arrangement for generating masks in fine-area correction (also referred to as selective color correction or color retouch) for image processing. Methods for generating masks are already known from the prior art. One possibility is comprised in placing a mask (often also referred to as "lasso") around a color to be corrected in the image, as shown in FIG. 1. An area in the image that contains the selected color is traced with the cursor and a geometric mask is thus produced. The color correction then only acts on the area inside the mask. The problem of this method is that very bright or very dark regions of the color are also covered. This can lead to an over-correction of the dark or light locations, which is noticed in the color-corrected image as disturbing color dots. Further, the demarcation of the mask in the image or the generating of the mask must occur very precisely, since the entire color area will otherwise not be covered, or an adjoining color that is not to be corrected is also covered. This then leads to color breaks at the locations in the image where different colors abut one another.
The German Patent Application of Linotype-Hell AG, DE-A-4311611.6 "Stuetzstellenkorrektur", filed 8 Apr. 1993, copending U.S. Ser. No. 08/224,473, filed Apr. 7, 1994, now U.S. Pat. No. 5,489,921, discloses that color samples be taken from an image. These color samples form an irregular collection of points, in what is referred to as a "cloud" in the color space. This cloud thereby determines the area of the colors that are subjected to a color correction. A mask for the colors in the image that lie within this cloud can now be generated with this cloud. A check must now be carried out for every picture element to see whether it lies inside the cloud. For that purpose, the color data of the color pixels are compared to those of the cloud. When coincidence is present, then the color pixel lies within the cloud and a mask is placed at this location. This method is complicated and computation-bound because every individual picture element is compared to the points of the cloud.